Re: [PATCH v2 1/1] perf: Sharing PMU counters across compatible events

[Jiri Olsa]

On Thu, Aug 30, 2018 at 06:51:07PM +0000, Song Liu wrote:
> 
> 
> > On Aug 30, 2018, at 8:18 AM, Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
> > 
> > On Wed, Aug 15, 2018 at 10:03:13AM -0700, Song Liu wrote:
> > 
> > SNIP
> > 
> >> @@ -6100,7 +6333,7 @@ static void perf_output_read_group(struct perf_output_handle *handle,
> >> 
> >> 		if ((sub != event) &&
> >> 		    (sub->state == PERF_EVENT_STATE_ACTIVE))
> >> -			sub->pmu->read(sub);
> >> +			event_pmu_read(sub);
> >> 
> >> 		values[n++] = perf_event_count(sub);
> >> 		if (read_format & PERF_FORMAT_ID)
> >> @@ -9109,7 +9342,7 @@ static enum hrtimer_restart perf_swevent_hrtimer(struct hrtimer *hrtimer)
> >> 	if (event->state != PERF_EVENT_STATE_ACTIVE)
> >> 		return HRTIMER_NORESTART;
> >> 
> >> -	event->pmu->read(event);
> >> +	event_pmu_read(event);
> >> 
> >> 	perf_sample_data_init(&data, 0, event->hw.last_period);
> >> 	regs = get_irq_regs();
> >> @@ -10504,6 +10737,14 @@ SYSCALL_DEFINE5(perf_event_open,
> >> 		goto err_cred;
> >> 	}
> >> 
> >> +	if (perf_event_can_share(event)) {
> >> +		event->tmp_master = perf_event_alloc(&event->attr, cpu,
> >> +						     task, NULL, NULL,
> >> +						     NULL, NULL, -1);
> > 
> > can't get around this.. I understand the need, but AFAICS you allocate
> > the whole 'struct perf_event', just because there's count field in it
> > otherwise the 'struct hw_perf_event' should be enough to carry all that's
> > needed to read hw event
> > 
> > would it be better to move the count to 'struct hw_perf_event' and use
> > that instead? assuming I'm not missing anything..
> > 
> > jirka
> 
> I am trying to make the master event function the same as a real event, 
> while keep dup events as followers. This avoids "switching master" in 
> earlier versions (and Tejun's RFC). 

yep, I understand.. still, it seems too much to allocate
the whole 'struct perf_even't just to get separated 'count'
variable

jirka